1. Field of the Invention
The present invention relates to an automatic analyzer and automatic analyzing method which carries out qualitative and quantitative analyses of biological or chemical samples such as blood and urine and more particularly to an automatic analyzer with a mixing device.
2. Description of the Related Art
It is known that conventional chemical or biochemical analyzers use a reaction liquid obtained by mixing a sample such as a serum with a desired reagent as an object of analysis and further measure its absorbance. This kind of analyzer is comprised of a mechanism for providing a sample and a reagent into a reaction chamber or cuvette, a mechanism for mixing a sample and a reagent in a reaction chamber, a mechanism for analyzing physical properties of a sample which is reacting or has finished reaction, and so on.
A major technical problem in analyzers is reduction of the required quantities of sample and reagent for analysis. One reason for this is that as the number of test items increases, the quantity of sample available for one test item decreases. For example, in blood tests of infants, the quantity of blood sample available for analysis is very small. In addition, from the viewpoint of cost, there is a demand for the reduction in the quantity of reagent used in analysis. This is due to the growing tendency that advanced analysis techniques are introduced and expensive reagents are widely used.
As the quantities of sample and reagent used for analysis were decreased, the size of reaction chambers were reduced accordingly. However, this has led to a new problem. For example, when the reaction liquid is mixed mechanically by a spatula or the like, the ratio of reaction liquid taken out or the ratio of rinse fluid taken in becomes larger, which affects the analysis result. One solution to this problem related to mixing is a non-contact mixing device using ultrasonic waves as described in JP-A No. 2003-35715. However, in this case, for the sample and reagent which are injected into a reaction chamber, their mixture ratio varies depending on the type of test, or test item. So the quantity of liquid to be measured in the chamber is different and complicated control work is needed for accomplishing efficient mixing.
The technique described in JP-A No. 2003-35715 uses a plurality of ultrasonic oscillators provided at different heights so that mixing efficiency does not deteriorate even when the liquid level of liquid to be mixed varies. In this case, complicated control work is needed to determine which oscillator should be activated according to the liquid level. Also it is desirable to adjust the oscillation intensity depending on the properties of the liquid to be mixed (viscosity, etc). Not only in non-contact ultrasonic mixing but also in mechanical mixing with a spatula, a smaller quantity of liquid to be mixed makes it more difficult to ensure uniformity in mixing.
An object of the present invention is to provide an automatic analyzer and analyzing method having a mixing device with a simple structure which is able to mix liquids uniformly regardless of the quantity of sample present and liquid properties thereof.